1. Field of the Invention
The invention relates generally to a storage system and access count equalization method for the storage system and is suitable for use in, for example, a storage system having a function of migrating data between parity groups, from a high-use parity group to a low-use parity group, and an access count equalization method for the storage system.
2. Description of Related Art
With the rapid increase in the amount of data in storage systems, users are required, at regular time intervals, to consider redesigning databases in the storage systems, including table definition and data size definition, as well as the review of the configurations of their storage systems, including system definition. The result of such a review of the system configuration may sometimes show unevenness in data access counts.
In order to solve the unevenness in the data access counts, a function called ‘volume migration’ that equalizes the data access counts to optimize a storage system (for example, see Patent Document 1) has been in existence. With the volume migration function, which uses virtual volumes, a system administrator for the storage system is capable of migrating data between parity groups, from a high-use parity group to a low-use parity group, either in units of volumes (logical devices) or in units of pages.    [Patent Document 1] JP2001-067187 A
However, although the above volume migration function is capable of migrating data from a high-use parity group to a low-use parity group either in units of volumes or in units of pages, it cannot judge which data migration—data migration in units of volumes or data migration in units of pages—is more suitable. Therefore, although system administrators can have their storage systems perform the volume migration function by selecting either of the data migration methods, they never be sure that if they are having the storage systems perform the optimal volume migration function.
This invention has been devised in light of the above points and aims to suggest a storage system capable of equalizing the access counts in the most appropriate units to optimize the entire storage system, and an access count equalization method for the storage system.